Hot melt composition in the form of a film for use in thin film photovoltaic modules

ABSTRACT

The invention features a hot melt composition in the form of a film including from 40% by weight to 80% by weight of a non-functionalized alkyl acrylate, from 14% by weight to 50% by weight of an olefin polymer, from 2% by weight to 15% by weight of a first functionalized polymer comprising a functional group selected from the group consisting of epoxides and carboxylic anhydrides, and from 2% by weight to 15% by weight of a second functionalized polymer comprising a functional group capable of reacting with the functional group of the first functionalized polymer. 
     The hot melt composition in the form of a film has found utility as an encapsulant for thin film photovoltaic modules.

This application is a Continuation of U.S. patent application Ser. No.17/659,422, filed Apr. 15, 2022 which claims the benefit of U.S.Provisional Patent Application No. 63/201,167 filed on Apr. 15, 2021which is incorporated herein.

BACKGROUND

A crystalline silicon photovoltaic (PV) module commonly includes aphotovoltaic layer, usually mono or multi-crystalline silicon, laminatedbetween two encapsulant layers, with a thick glass substrate as thefront layer and a protective back sheet. Additional layers can be foundbetween these layers e.g. tie layers and adhesives. The crystalline PVmodule is rigid. The crystalline PV module can often have a breathableconstruct i.e. there is no seal holding it together at the edges. Assuch, low cost encapsulants e.g. peroxide cured alkyl acetates can beused since left over peroxide material can diffuse through the edgesinto the atmosphere and thus not harm the module.

A thin film PV module includes photovoltaic cells that are thinner andless expensive. A thin film PV module commonly includes a front sheet onwhich the photovoltaic cells can be deposited, an encapsulant, and aback sheet. The photovoltaic cells within the thin film PV module can bearound 350 times thinner than those in the crystalline PV module. Thisgives the thin film PV module the advantage of being lighter and moremaneuverable as compared to the crystalline silicon PV module. However,since there is generally an edge seal present around the outer edge of athin film PV module, materials such as peroxide, or polymers that breakdown to form acid e.g. ethylene vinyl acetate cannot be used in theencapsulant. This is because the materials that form would be trapped inthe module and could damage it. Further, in the thin film PV modulesince there is often only one layer of encapsulant, there is anincreased stress put on the encapsulant.

There is a need for encapsulants for thin film PV modules that are freeof materials that can contaminate the module e.g. peroxides, acids,etc., provide a balance of heat resistance and adhesion, withstandenvironmental changes and are economical in cost.

SUMMARY

In one aspect, the invention features a hot melt composition in the formof a film including from 40% by weight to 80% by weight of anon-functionalized alkyl acrylate, from 14% by weight to 50% by weightof an olefin polymer, from 2% by weight to 15% by weight of a firstfunctionalized polymer comprising a functional group selected from thegroup consisting of epoxides, carboxylic anhydrides and carboxylicacids, and from 2% by weight to 15% by weight of a second functionalizedpolymer comprising a functional group capable of reacting with thefunctional group of the first functionalized polymer.

In one embodiment, the hot melt composition has an Approximate MeltIndex of from 5 g/10 min to 80 g/10 min. In another embodiment, thenon-functionalized alkyl acrylate is selected from the group consistingof ethylene n-butyl acrylate and ethylene methyl acrylate. In adifferent embodiment, the non-functionalized alkyl acrylate is ethylenen-butyl acrylate. In one embodiment, the ethylene n-butyl acrylate hasan n-butyl acrylate content of from 3% by weight to 35% by weight. Inanother embodiment, the ethylene n-butyl acrylate has a Melt Index offrom 5 g/10 min to 50 g/10 min when tested by ASTM D 1238 (190° C., 2.16kg). In one embodiment, the olefin polymer is a single-site catalyzedethylene copolymer.

In another embodiment, the olefin polymer has a density as testedaccording to ASTM D 792 of no greater than 0.92 g/cm³. In oneembodiment, the first functionalized copolymer and the secondfunctionalized copolymer are ethylene copolymers.

In a different embodiment, the first functionalized polymer is selectedfrom the group consisting of a random copolymer of ethylene and maleicanhydride, a random copolymer of ethylene, alkyl(meth)acrylate andmaleic anhydride and, the second functionalized polymer is selected froma group consisting of a random copolymer of ethylene and glycidylmethacrylate and a random terpolymer of ethylene, alkyl(meth)acrylateand glycidyl methacrylate.

In one embodiment, the hot melt composition is free of ethylene vinylacetate, peroxide, and poly vinyl chloride. In another embodiment, thehot melt composition includes from 55% by weight to 75% by weight of anon-functionalized alkyl acrylate, from 15% by weight to 25% by weightof an olefin, from 3% by weight to 10% by weight of a firstfunctionalized polymer comprising a functional group selected from thegroup consisting of epoxides and carboxylic anhydrides, and from 3% byweight to 10% by weight of a second functionalized polymer comprising afunctional group capable of reacting with the functional group of thefirst functionalized polymer.

In one embodiment, the hot melt composition further includes a silaneadhesion promoter. In another embodiment, the hot melt compositionfurther includes from 5% by weight to 50% by weight of a filler.

In one embodiment, the invention includes a thin film photovoltaicmodule comprising the hot melt composition. In another embodiment, theinvention includes a thin film photovoltaic module including a frontsheet, a layer of photovoltaic cells in contact with the front sheet,the hot melt composition in the form of a film, and a back sheet,wherein the hot melt composition in the form of a film is locatedbetween the photovoltaic cells and the back sheet and adheres the frontsheet to the back sheet.

In another embodiment, the photovoltaic cells are selected from thegroup consisting of CIGS (copper indium gallium diselenide), CdTe(cadmium telluride), amorphous thin-film silicon (a-Si, TF-Si), copperindium disilenide (CIS), and perovskite based systems.

In a different embodiment, the thin film photovoltaic module furthercomprises an edge seal. In another embodiment, the back sheet and thefront sheet are glass and the photovoltaic cells are CdTe.

The hot melt films of this invention have been found to have an idealbalance of heat resistance and adhesion in that they can be used as anencapsulant in thin film PV modules resulting in a module that canwithstand environmental changes while being economical in cost.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graphical representation of the storage modulus data inTable 1.

DETAILED DESCRIPTION Hot Melt Composition

This invention is directed to a hot melt composition in the form of afilm (sometimes referred to as a sheet) including non-functionalizedethylene/alkyl acrylate copolymer, an olefin polymer and a combinationof functionalized polymers.

The hot melt composition in the form of a film can include from 40% byweight to 80% by weight of a non-functionalized alkyl acrylate, from 14%by weight to 50% by weight of an olefin polymer, from 3% by weight to15% by weight of a first functionalized polymer comprising a functionalgroup selected from the group consisting of epoxides, carboxylicanhydrides and carboxylic acids, and from 3% by weight to 15% by weightof a second functionalized polymer comprising a functional group capableof reacting with the functional group of the first functionalizedpolymer.

The hot melt composition in the form of a film can include from 40% byweight to 80% by weight of a non-functionalized alkyl acrylate, from 14%by weight to 50% by weight of an olefin polymer, from 2% by weight to15% by weight of a first functionalized polymer comprising a functionalgroup selected from the group consisting of epoxides, carboxylicanhydrides and carboxylic acids, and from 2% by weight to 15% by weightof a second functionalized polymer comprising a functional group capableof reacting with the functional group of the first functionalizedpolymer.

The hot melt composition can include a significant amount of anon-functionalized copolymer of ethylene and alkyl acrylate, asingle-site catalyzed olefin polymer having a density as testedaccording to ASTM D 792 of no greater than 0.92 g/cm³, and a limitedamount of two different functionalized polymers.

The hot melt composition can include from 40% by weight to 74% by weightof a non-functionalized alkyl acrylate, from 14% by weight to 50% byweight of a single-site catalyzed ethylene copolymer having a density astested according to ASTM D 792 of from 0.85 g/cm³ to 0.92 g/cm³, from 2%by weight to 15% by weight of a first functionalized polymer comprisinga functional group selected from the group consisting of epoxides,carboxylic anhydrides and carboxylic acids, and from 2% by weight to 15%by weight of a second functionalized polymer comprising a functionalgroup capable of reacting with the functional group of the firstfunctionalized polymer.

The hot melt composition can include from 40% by weight to 74% by weightof a non-functionalized alkyl acrylate, from 14% by weight to 50% byweight of a single-site catalyzed ethylene copolymer having a density astested according to ASTM D 792 of from 0.85 g/cm³ to 0.92 g/cm³, from 3%by weight to 15% by weight of a first functionalized polymer that is acopolymer of ethylene and an epoxy group and from 3% by weight to 15% byweight of a second functionalized polymer that is a copolymer ofethylene and at least one monomer selected from the group consisting ofa carboxylic anhydride, a carboxylic acid, and combinations thereof.

The non-functionalized alkyl acrylate, the olefin polymer, the firstfunctionalized polymer and the second functionalized polymer cancomprise at least 80% by weight, at least 90% by weight, at least 95% byweight, from 80% by weight to 100% by weight or even from 90% by weightto 100% by weight of the hot melt composition.

The hot melt composition can be free of peroxides, ethylene vinylacetate and poly vinyl chloride (PVC).

The hot melt composition can have an Approximate Melt Index of from 0.5to 50 g/10 minutes (min), 5 to 50 g/10 min, or even from 10 to 30 g/10min.

The inventors have discovered that the hot melt composition needs tohave a relatively low storage modulus at a temperature range of between0° C. and −50° C., or even between −20° C. and −50° C. to improveperformance in response to changes in the environment (e.g. freeze/thawcycles, changes in humidity, etc.). Storage modulus is a mechanicalmeasure of the stiffness of a solid material.

The hot melt composition can have a storage modulus at a temperature of−40° C. of no greater than 1,100 megapascals (MPa), no greater than1,050 MPa, no greater than 1,000 MPa, no greater than 900 MPa, from 100MPa to 1,100 MPa, from 200 MPa to 1,050 MPa, from 300 MPa to 1,100 MPa,or even from 400 MPa to 1,100 MPa.

Non-Functionalized Ethylene Alkyl Acrylate Copolymer

The hot melt composition includes a significant amount of anon-functionalized copolymer of ethylene and an alkyl acrylate. Themajority of the hot melt composition can comprise a non-functionalizedethylene alkyl acrylate copolymer. The hot melt composition can includemore than one non-functionalized ethylene alkyl acrylate copolymer.

The alkyl acrylate can be selected from the group consisting ofunsaturated carboxylic acid esters such as methyl acrylate, ethylacrylate, isopropyl acrylate, n-butyl acrylate, isooctyl acrylate,methyl methacrylate, 2-ethylhexyl acrylate and isobutyl acrylate.

Preferred non-functionalized ethylene alkyl acrylate copolymers can beselected from the group consisting of ethylene n-butyl acrylate,ethylene methacrylate and ethylene methyl methacrylate.

The non-functionalized ethylene alkyl acrylate copolymer can have analkyl acrylate content of from 3% by weight to 40% by weight, from 3% byweight to 35% by weight, from 10% by weight to 35% by weight, or evenfrom 15% by weight to 30% by weight.

The non-functionalized ethylene alkyl acrylate copolymer can have a meltindex of from 5 g/10 min to 100 g/10 min, from 5 g/10 min to 75 g/10min, from 5 g/10 min to 50 g/10 min, or even from 5 g/10 min to 40 g/10min as tested according to ASTM D1238 (190° C., 2.16 kg).

The non-functionalized ethylene alkyl acryate copolymer will preferablybe obtained according to a “tubular” polymerization process.

Useful non-functionalized ethylene alkyl acrylate copolymers includethose sold under the EBAC and EMAC trade designations such as EBACSB2811, an ethylene n-butyl acrylate copolymer having a melt index of 20g/10 min as tested according to ASTM D1238 (190° C., 2.16 kg) and ann-butyl acrylate content of 20% by weight, and EMAC SP2220, an ethylenemethacrylate copolymer having a melt index of 20 g/10 min as testedaccording to ASTM D1238 (190° C., 2.16 kg) and an methacrylate contentof 20% by weight both available from Westlake Polymers LLC (Houston,Tex.), EBANTIX E20020, an ethylene n-butyl acrylate copolymer having amelt index of 20 g/10 min as tested according to ASTM D1238 (190° C.,2.16 kg) and an n-butyl acrylate content of 20% by weight, availablefrom Repsol Chemicals (Madrid, Spain) and LOTRYL 35BA40, an ethylenen-butyl acrylate copolymer, available from SK Functional Polymer(Courbevoie, France)

The hot melt composition includes from 40% by weight to 80% by weight,from 40% by weight to 74% by weight, from 50% by weight to 80% byweight, from 55% by weight to 80% by weight, from 55% by weigh to 74% byweight, from 60% by weight to 80% by weight, or even from 60% by weightto 74% by weight of the non-functionalized ethylene alkyl acrylatecopolymer.

Olefin Copolymer

The olefin copolymer functions to lower the modulus (or stiffness) ofthe composition and improve performance in response to changes in theenvironment (e.g. freeze/thaw cycles, changes in humidity, etc.)

The olefin copolymer can be a copolymer of ethylene and an alpha-olefin.The alpha-olefin can have from 3 to 30 carbon atoms. The alpha olefincan be selected from the group consisting of propylene, 1-butene,1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene,3-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene,1-hexadecene, 1-octadecene, 1-eicosene, 1-docosene, 1-tetracosene,1-hexacosene, 1-octacosene and 1-triacontene.

The olefin polymer can be polymerized by known polymerization techniquese.g. Ziegler-Natta or single-site (e.g. metallocene) catalysis. In apreferred embodiment, the olefin polymer is polymerized by a single-site(e.g. metallocene) catalyst.

The olefin polymer can be functionalized i.e. modified with a functionalgroup such as e.g. maleic anhydride, however in a preferred embodimentit is non-functionalized.

The olefin polymer can have a Mw/Mn ratio of no greater than 5, nogreater than 3, or even no greater than 2, in which Mw and Mnrespectively denote the weight-average molar mass and the number-averagemolar mass.

The olefin polymer can have a density as tested according to ASTM D 792of no greater than 0.92 g/cm³, no greater than 0.91 g/cm³, no greaterthan 0.89 g/cm³, no greater than 0.88 g/cm³, from 0.85 g/cm³ to 0.92g/cm³, or even from 0.85 g/cm³ to 0.90 g/cm³.

The olefin polymer can have a melt index of from 5 g/10 min to 100 g/10min, from 5 g/10 min to 75 g/10 min, from 5 g/10 min to 50 g/10 min, oreven from 5 g/10 min to 40 g/10 min as tested according to ASTM D1238(190° C., 2.16 kg).

Useful olefin polymers include the ENGAGE series of polymers, includingENGAGE 8411, an ethylene-octene copolymer having a density of 0.88 g/cm³and a melt index of 18 g/10 min as tested according to ASTM D1238 (190°C., 2.16 kg) and ENGAGE PV8658, an ethylene-octene copolymer have adensity of 0.90 g/cm³ and a melt index of 30 g/10 min as testedaccording to ASTM D1238 (190° C., 2.16 kg) both available from The DowChemical Company (Midland, Mich.) and the SOLUMER series of polymers,including SOLUMER 8613, an ethylene-octene copolymer having a density of0.863 g/cm³ and a melt index of 13 g/10 min as tested according to ASTMD1238 (190° C., 2.16 kg) available from SK Innovation Co., Ltd. (Seoul,Korea).

The hot melt composition can include from 14% by weight to 60% byweight, from 14% by weight to 55% by weight, from 14% by weight to 50%by weight, from 14% by weight to 45% by weight, from 14% by weight to40% by weight, or even from 14% by weight to 30% by weight of the olefinpolymer.

The hot melt composition can include from 16% by weight to 60% byweight, from 16% by weight to 55% by weight, from 16% by weight to 50%by weight, from 16% by weight to 45% by weight, from 16% by weight to40% by weight, or even from 16% by weight to 30% by weight of the olefinpolymer.

Functionalized Polymers

The inventors have found that functionalized polymers are important inorder to maintain the heat resistance of the hot melt composition.

The hot melt composition of this invention includes at least twofunctionalized polymers. The two functionalized polymers are chosen tohave functional groups that react with each other. The inventorstheorize that the reacted polymers form a network throughout thecomposition that results in increased heat resistance. The inventorshave unexpectedly discovered that this network is still formed even whenlimited amounts of the functionalized polymers are used. Thefunctionalized polymers can be copolymers of ethylene and variousfunctional groups.

In a preferred embodiment, the hot melt composition is substantiallyfree of curing agents. Curing agents include any species other than thefirst functionalized polymer and the second functionalized polymer thatfacilitates or is involved in the curing reaction of the functionalizedpolymers. Curing agents include materials such as e.g. peroxides,amines, phenols, etc.

The first functionalized polymer includes a functional group selectedfrom the group consisting of carboxylic anhydrides, carboxylic acids,epoxy groups and combinations thereof.

The first functionalized polymer can include ethylene and a carboxylicacid anhydride functional group. The carboxylic acid anhydridefunctional group can be chosen, from maleic, itaconic, citraconic,allylsuccinic, cyclohex-4-ene-1,2-dicarboxylic,4-methylenecyclohex-4-ene-1,2-dicarboxylic,bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic andx-methylbicyclo[2.2.1]hept-5-ene-2,2-dicarboxylic anhydrides.

The first functionalized polymer can include ethylene and a carboxylicacid. The carboxylic acid can be chosen from the group consisting ofacrylic acid and methacrylic acid.

The first functionalized polymer can include ethylene and an epoxygroup. Examples of epoxy-containing monomer units include aliphaticesters and glycidyl ethers such as an allyl glycidyl ether, a vinylglycidyl ether, a maleate or itaconate of glycidyl, a glycidylmethacrylate, and alicyclic esters and glycidyl ethers, such as a2-cyclohexene-1-glycidyl ether, a cyclohexene-4, 5-diglycidylcarboxylate, a cyclohexene-4 glycidyl carboxylate, a5-norbomene-2-methyl-2-glycidyl carboxylate and an endo cis-bicyclo(2,2,1)-5-heptene-2,3-diglycidyl dicarboxylate.

The epoxy-containing monomer unit is preferably incorporated as acomonomer, i.e. by copolymerizing an olefin monomer with the vinyl groupcontaining comonomer bearing an epoxy group (=epoxy-group containingmonomer unit). Most preferably, the epoxy-group-containing monomer unitsare glycidyl methacrylate comonomer units.

The second functionalized polymer includes a functional group capable ofreacting with the functional group of the first functionalized polymer.

The first functionalized polymer and/or the second functionalizedpolymer can be functionalized alkyl(meth)acrylates. Preference is givento alkyl(meth)acrylates having an alkyl chain comprising from 1 to 4carbon atoms, preferably methyl, ethyl or butyl.

Alternatively, the first functionalized polymer and/or the secondfunctionalized polymer can be functionalized ethylene alpha olefincopolymers such as e.g. single site catalyzed ethylene alpha olefincopolymers functionalized with maleic anhydride, glycidyl methacrylate,etc.).

The first functionalized polymer can be a copolymer of ethylene and anepoxy group and the second functionalized polymer can a copolymer ofethylene and at least one monomer selected from the group consisting ofa carboxylic anhydride, a carboxylic acid, and combinations thereof.

The first functionalized polymer can be a random copolymer of ethyleneand of maleic anhydride or a random copolymer of ethylene, of alkylmethacrylate and of maleic anhydride and the second functionalizedpolymer can be a random copolymer of ethylene and of glycidylmethacrylate or a random terpolymer of ethylene, of alkyl methacrylateand of glycidyl methacrylate.

The functionalized polymers can be formed by radical polymerizationprocesses at high pressure in an autoclave reactor or in a tubularreactor, which are techniques known to a person skilled in the art.

The functionalized polymers can have a melt flow index as tested by ASTMD 1238 (190° C., 2.16 kg) of from 2 g/10 min to 500 g/10 min, from 2g/10 min to 100 g/10 min, or even from 2 g/10 min to 50 g/10 min.

Useful functionalized polymers include those available under the LOTADERtrade designation including LOTADER 4210, an ethylene butyl acrylatemaleic anhydride terpolymer, having 6.5% by weight butyl acrylate, 3.6%by weight maleic anhydride and a melt flow index of 10 g/10 min astested by ASTM D 1238 (190° C., 2.16 kg) and LOTADER AX 8840, anethylene glycidyl methacrylate copolymer, having 6-8% by weight glycidylmethacrylate and a melt flow index of 5 g/10 min as tested by ASTM D1238 (190° C., 2.16 kg), both available from SK Functional Polymer(Courbevoie, France), NUCREL 0910, an ethylene methacrylic acidcopolymer, having 8.7% by weight methacrylic acid and a melt flow indexof 10 g/10 min as tested by ASTM D 1238 (190° C., 2.16 kg), ELVALOY4170, an ethylene terpolymer having a melt flow index of 8 g/10 min astested by ASTM D 1238 (190° C., 2.16 kg), and FUSABOND M603, a maleicanhydride functionalized ethylene copolymer having a melt flow index of25 g/10 min as tested by ASTM D 1238 (190° C., 2.16 kg) all availablefrom Dow Chemical (Houston, Tex.).

The hot melt composition includes from 2% by weight to 15% by weight,from 3% by weight to 15% by weight, from 2% by weight to 10% by weight,from 3% by weight to 10% by weight, or even from 3% by weight to 7.5% byweight of the first functionalized polymer and from 2% by weight to 15%by weight, from 3% by weight to 15% by weight, from 2% by weight to 10%by weight, from 3% by weight to 10%, or even from 3% by weight to 7.5%by weight of the second functionalized polymer.

Silane Adhesion Promoter

The hot melt adhesive composition can include a silane adhesionpromoter. The silane adhesion promoter helps improve adhesion betweenthe encapsulant and the glass. The silane adhesion promoter is notlimited and can include any type of silane composition useful inpromoting the adhesion of the hot melt composition to a substrate.

The silane adhesion promoter can be selected from the group consistingof a silane, an amino silane, an epoxy silane, an isocyanurate silaneand any other silane.

The hot melt composition can include from 0.05% by weight to 5% byweight, from 0.1% to 3% by weight, or even from 0.2% by weight to 2% byweight of the silane adhesion promoter.

Useful silane adhesion promoters include those available under theDYNASYLAN trade designation, include DYNASYLAN GLYMO, a bifunctionalorganosilane possessing a reactive organic epoxide and hydrolyzableinorganic methoxysilyl groups, DYNASYLAN AMMO,3-(trimethoxysilyl)propylamine and DYNASYLAN VPS7161, isocyanuratesilane with a high concentration of trimethoxysilyl groups all availablefrom Evonik GmBH (Hanau, Germany) and COATOSIL MP200, an epoxyfunctional silane oligomer available from Momentive PerformanceMaterials Inc.

Fillers

The hot melt composition can include a filler. The filler can beselected from the group consisting of silica, treated silica, alumina,calcium carbonate, barium sulfate, zinc oxide, clay, talc, carbonnanotubes and carbon black. The hot melt composition can alternativelyinclude any other filler.

The composition can include up to 50% by weight, from 5% by weight to50%, from 5% by weight to 30% by weight, or even from 5% by weight to20% by weight of a filler.

Optional Components

The hot melt composition can include optional components such as e.g. UVstabilizers (e.g. benzophenone, benzotriazole, etc.), antioxidants,hindered amine light stabilizers (HALS), flame retardants, tackifyingresins, other polymers (e.g. LDPE, other olefin polymers, acrylics(JONCRYL ADR, etc.), other pigments, dyes and optical brighteners.

Useful commercially available UV stabilizers include CYABSORB UV531 andCYAB SORB UV 9, available from Solvay S.A. (Brussels, Belgium).

Method of Making

The hot melt composition can be made by blending the required materialswith the optional additives using known techniques for blendingthermoplastics, such as, for example, extrusion or kneading. Usefulmethods of extrusion or kneading include internal blade or rotor mixers,an external mixer, or single-screw or corotating or counterrotatingtwin-screw extruder.

Hot Melt Composition in the Form of a Film

The hot melt composition is preferably used in the form of a film. Thefilm can have a thickness ranging from 0.1 mm to 20 mm, from 0.2 mm to20 mm, or even from 0.5 mm to 10 mm.

The functionalized polymers will begin to react as they are made into afilm and will continue to react in the process by which the module ismade.

The film can be a monolayer (i.e. one layer consisting of the hot meltcomposition) or a multilayer. When it is multilayer, the hot meltcomposition can be present as two or more films or can be combined withlayers of other materials conventionally used in the photovoltaic fielde.g. polyolefins, ionomers, fluoropolymers, etc.

The film can be obtained by a method selected from the group consistingof pressing, tubular (bubble) extrusion-blow molding,extrusion-laminating, extrusion-coating, flat sheet extrusion (alsoknown as extrusion-casting) and calendaring. When extruded, agravimetric feeder can be used to feed the various materials into theextruder.

Thin Film PV Module

The hot melt composition in the form of a film can serve as anencapsulant in a thin film PV module.

The thin film PV module can include a front sheet on which thephotovoltaic cells can be deposited, the hot melt composition in theform of a film as an encapsulant, and a back sheet. The hot meltcomposition in the form of a film is located between the front sheet andthe back sheet and adheres the assembly together.

The front sheet needs to be transparent. The front sheet can becomprised of glass or a transparent plastic (e.g. poly methylmethacrylate, polytetrafluoroethylene (ptfe),poly(ethene-co-tetrafluoroethene) (etfe), polyester, or any othertransparent plastic).

The photovoltaic cells can be deposited on the front sheet, back sheet,or a separate substrate such as e.g. metal film. The photovoltaic cellcan comprise a number of materials e.g. CIGS (copper indium galliumdiselenide), CdTe (cadmium telluride), amorphous thin-film silicon(a-Si, TF-Si), copper indium disilenide (CIS), organics and perovskite.

In some thin film PV modules, when the photovoltaic cells are depositedon the front sheet, the encapsulant does not need to be transparent.

The back sheet can comprise glass, plastic or metal. The back sheet canbe flexible or not flexible.

In one embodiment, the front sheet and the back sheet are glass, thephotovoltaic cells comprise CdTe and are deposited on the front sheetand the hot melt composition in the form of a film bonds the assemblytogether.

The thin film PV module can further include an edge seal. The edge sealis a material that forms a seal between the outer edges of the frontsheet and back sheet to provide an extra barrier to prevent moisturefrom weakening the structure of the module or damaging the cells. Theedge seal is commonly based on butyl rubber but could alternately bebased on polyisobutylene. The edge seal can further include a desiccantmaterial.

The various layers can be assembled by any type of pressing technique,such as, for example, hot pressing, vacuum pressing or laminating (e.g.heat laminating). The thin film PV module can be laminated attemperatures of from 120° C. to 180° C., or even at temperature of from140° C. to 170° C.

The invention will now be described by way of the following examples.All parts, ratios, percents and amounts stated in the Examples are byweight unless otherwise specified.

Examples Test Procedures

Test procedures used in the examples and throughout the specification,unless stated otherwise, include the following. The amounts of rawmaterials listed in Table 1 are in weight percent.

Approximate Melt Index

For the samples in Table One an approximate Melt Index was arrived uponbased on the melt index ASTM D 1238 (190° C., 2.16 kg) of the variouscomponents as reported by their suppliers, using a calculated weightedaverage. For example, MI of Ex 1=MI of EBAC SB2811*(72.37/100)+MI ofLOTADER AX 8840*(4.5/100)+MI of LOTADER 4210*(4.5/100)+MI of ENGAGE8411*(18/100)

Storage Modulus

The Storage Modulus was obtained by a dynamic mechanical analysis (DMA)temperature sweep using a TA (Thermal Analysis) Instruments Inc. dynamicmechanical analyzer. The following method was used. The sample wasequilibrated at −100° C. for 0.15 minutes and then heated at 3°C./minute at 1 Hz with a static load of 0.1 Newtons to 100° C.

TABLE 1 Comp 1 Comp 2 Comp 3 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 EBAC SB281179.67 78.67 74.8 72.37 63.37 54.37 45.37 62.9 LOTADER AX 8840 3.9 3.65.4 4.5 4.5 4.5 4.5 LOTADER 4210 3.9 3.6 5.4 4.5 4.5 4.5 4.5 FUSABONDM603 6.74 ELVALOY 4170 2.7 ENGAGE 8411 11.9 13.5 13.5 18 27 36 45 26.94DYNASYLAN .45 .45 .45 .45 .45 .45 .45 0.45 GLYMO CYABSORB UV531 .18 .18.45 .18 .18 .18 .18 CYABSORB UV 9 0.27 Approximate Melt Index 18.7 18.718.2 18.4 18.2 18.0 17.8 19.3 (g/10 min) Storage Modulus (MPa) @−50° C.1861 1691 1727 1394 1286 @−40° C. 1342 1128 1139 818.6 717.1 @−30° C.651.2 515.5 579.1 364.4 327.3 @−20° C. 346 283.3 309.4 176.1 178.6 @−10°C. 205.4 182.5 218.6 101.2 121.1  @ 0° C. 146.8 126.2 161.5 71.35 91.85

FIG. 1 shows a graphical representation of the storage modulus data. InFIG. 1 , it is clear that Ex 1 and Ex 2 have a relatively lower storagemodulus when compared to Comp 1, 2 and 3 at a temperature range ofbetween 0° C. and −50° C.

The inventors have found that the relatively lower storage modulus of Ex1 and Ex 2 (as compared to Comp 1, 2 and 3) enabled Ex 1 and Ex 2 tohave improved performance in Humidity/Freeze cycling when used as anencapsulant in a thin film PV module.

In Humidity/Freeze cycling, the panel spends 20 hours at 85° C.+85%Relative Humidity, then is cooled to −40° C. for 4 hours. Each 24-hourperiod is 1 cycle. As a typical industry standard, the panel needs toremain defect free for at least 10, or even at least 20 cycles.

Other embodiments are within the claims.

What is claimed is:
 1. A hot melt composition in the form of a filmcomprising: a. from 40% by weight to 80% by weight of anon-functionalized alkyl acrylate, b. from 14% by weight to 50% byweight of an olefin polymer comprising a copolymer of ethylene andpropylene, c. from 2% by weight to 15% by weight of a firstfunctionalized polymer comprising a functional group selected from thegroup consisting of epoxides, carboxylic anhydrides and carboxylicacids, and d. from 2% by weight to 15% by weight of a secondfunctionalized polymer comprising a functional group capable of reactingwith the functional group of the first functionalized polymer.
 2. Thehot melt composition of claim 1 wherein the olefin polymer has a MeltIndex of from 5 g/10 min to 100 g/10 min as tested according to ASTMD1238 (190° C., 2.16 kg).
 3. The hot melt composition of claim 1 whereinthe olefin polymer has a Melt Index of from 5 g/10 min to 40 g/10 min astested according to ASTM D1238 (190° C., 2.16 kg).
 4. The hot meltcomposition of claim 1 wherein in the olefin polymer has a density offrom 0.85 g/cm3 to 0.90 g/cm3.
 5. The hot melt composition of claim 1wherein the olefin polymer is polymerized by single-site catalysis. 6.The hot melt composition of claim 1 wherein the olefin polymer ispolymerized by Ziegler-Natta catalysis.
 7. The hot melt composition ofclaim 1 wherein the olefin polymer further comprises an olefin polymerselected from the group consisting of a copolymer of ethylene andoctene, a copolymer of ethylene and butene and a copolymer of ethyleneand hexene.
 8. The hot melt composition of claim 1 having an approximateMelt Index of from 5 g/10 min to 80 g/10 min.
 9. The hot meltcomposition of claim 1 wherein the non-functionalized alkyl acrylate isselected from the group consisting of ethylene n-butyl acrylate andethylene methyl acrylate.
 10. The hot melt composition of claim 1wherein the non-functionalized alkyl acrylate is an ethylene n-butylacrylate having a n-butyl acrylate content of from 3% by weight to 35%by weight and a Melt Index of from 5 g/10 min to 50 g/10 min when testedby ASTM D 1238 (190° C., 2.16 kg).
 11. The hot melt composition of claim1 wherein the first functionalized copolymer and the secondfunctionalized copolymer are ethylene copolymers.
 12. The hot meltcomposition of claim 1 wherein: the first functionalized polymer isselected from the group consisting of a random copolymer of ethylene andmaleic anhydride, a random copolymer of ethylene, alkyl(meth)acrylateand maleic anhydride and, the second functionalized polymer is selectedfrom a group consisting of a random copolymer of ethylene and glycidylmethacrylate and a random terpolymer of ethylene, alkyl(meth)acrylateand glycidyl methacrylate.
 13. The hot melt composition of claim 1 beingfree of ethylene vinyl acetate, peroxide, and poly vinyl chloride. 14.The hot melt composition of claim 1 comprising: from 55% by weight to75% by weight of the non-functionalized alkyl acrylate, from 15% byweight to 25% by weight of the olefin polymer, from 3% by weight to 10%by weight of the first functionalized polymer, and from 3% by weight to10% by weight of the second functionalized polymer.
 15. The hot meltcomposition of claim 1, further including a silane adhesion promoterselected from the group consisting of amino silane, epoxy silane, andisocyanurate silane.
 16. The hot melt composition of claim 1 furthercomprising from 5% by weight to 50% by weight of a filler.
 17. Aphotovoltaic module comprising the hot melt composition in the form of afilm of claim
 1. 18. The thin film photovoltaic module comprising: a. afront sheet, b. a layer of photovoltaic cells in contact with the frontsheet, c. the hot melt composition in the form of a film of claim 1, andd. a back sheet, wherein the hot melt composition in the form of a filmis located between the photovoltaic cells and the back sheet and adheresthe front sheet to the back sheet.
 19. The thin film photovoltaic moduleof claim 18 wherein the photovoltaic cells are selected from the groupconsisting of CIGS (copper indium gallium diselenide), CdTe (cadmiumtelluride), amorphous thin-film silicon (a-Si, TF-Si) and copper indiumdisilenide (CIS) and perovskite based systems.
 20. The thin filmphotovoltaic module of claim 18 further comprising an edge seal.